1. Field of the Invention
The present invention relates to a non-magnetic single-component toner and developing method using the same, used for developing electrostatic latent images formed on a photosensitive member by electrophotography and the like.
2. Description of Related Art
Examples of conventional developing methods used for electrophotography and the like include a two-component developing method in which a magnetic brush is formed by charging an insulating powder having a binder resin for its main component, namely an insulating toner, and a magnetic carrier by friction, and an electrostatic latent image formed on a photosensitive member is developed with the magnetic brush; a magnetic single-component developing method in which an electrostatic latent image is developed with a single-component toner comprised of magnetic toner alone; and a non-magnetic single-component developing method in which a non-magnetic toner is formed in a thin layer on a developing sleeve and then an electrostatic latent image is developed by contact or non-contact of the thin layer with a photosensitive member.
Among each of the above developing methods, the non-magnetic single-component method in particular makes it possible to reduce the size of the developing assembly since it does not need to use together with a magnetic carrier, and in comparison with the magnetic single-component developing method, has superior toner transfer properties, fixing properties, and charging stability, thereby this method recently attracts considerable attention.
However, the non-magnetic single-component developing method caused the occurrence of fusing of toner to the developing sleeve (developing roller) composed of a non-magnetic sleeve and to the layer regulating member in the form of a charging blade during continuous copying of a large number of sheets. As a result, the problem occurred in which the thickness of the toner layer on the surface of the developing roller became non-uniform, causing the formation of white streaks and black streaks on the image. This trend created a particularly serious problem in the case of fine toner devised in response to requirements for high-resolution of recorded images.
As a means of solving such problems, attempts were made to impart fluidity to a conventional non-magnetic single-component toner by adhering an external additive composed of silica to toner particles having as their main components a binder resin such as styrene/acrylate copolymer, a colorant, and an charge control agent as described in Japanese Unexamined Patent Application, First Publication, No. 2-163760, Japanese Unexamined Patent Application, First Publication, No. 2-300763, and Japanese Unexamined Patent Application, First Publication, No. 4-152354.
However, even through such means were used, not only was the above toner fusing phenomenon unable to be completely eliminated, but since the charging property of the silica change considerably according to the environmental atmosphere, with charging properties increasing under low temperature and low humidity and conversely decreasing under high temperature and high humidity, there was the problem of significant impairment of toner charging stability.
In light of the above problems of the conventional non-magnetic single-component toner and the developing method using the same, the object of the present invention is to provide a non-magnetic single-component toner and developing method using the same, that has suitable charging properties, anti-fusing properties and long life under all environmental atmosphere in non-magnetic single-component developing methods, and allows the obtaining of stable images having minimal background fogging, proper image density, no image density unevenness, and no voids in image (particularly on thick paper), and superior solid black reproducibility.
As a result of earnest studies to solve the above problems, the inventors of the present invention found in particular that a non-magnetic single-component toner in which silica A, the surface of which is treated with aminosilane, silica B, which is treated with silicone oil, and silicone oil are adhered is preferable, and created a developing method using this toner, in which development is performed by forming a thin layer of the non-magnetic single-component toner on the surface of a developing roller comprised of a non-magnetic sleeve.
Namely, the first aspect of the present invention is a non-magnetic single-component toner comprising: silica A having a specific surface area of 30 to 70 m2/g as determined by a BET method, and having a surface which is at least treated with aminosilane, silica B having a specific surface area of 100 m2/g or more, and having a surface which is treated with silicone oil, silicone oil, and toner particles containing a binder resin and a colorant wherein silica A, silica B, silicon oil are adhered to surfaces of the toner particles.
The second aspect of the present invention is the non-magnetic single-component toner according to the first aspect, wherein the surface of silica A is treated with aminosilane and hexamethyldisilazane.
The third aspect of the present invention is the non-magnetic single-component toner according to the first aspect, wherein the amount of silica A adhered to the toner particles is 0.1 to 0.5% by weight, and the amount of the silica B adhered to the toner particles is 0.3 to 2.0% by weight.
The fourth aspect of the present invention is the non-magnetic single-component toner according to the first aspect, wherein the ratio of silica A and the silica B is from 1:2 to 1:10.
The fifth aspect of the present invention is the non-magnetic single-component toner according to the first aspect, wherein the amount of the silicone oil adhered to the surface of the toner particles is 0.01 to 0.1% by weight.
In addition, the sixth aspect of the present invention is a developing method comprising: moving non-magnetic single-component toner to an electrostatic latent image of a photosensitive member installed adjacent to a non-magnetic sleeve and developing the electrostatic latent image by reversal development; wherein development is performed by forming a thin layer of the non-magnetic single-component toner according to the first aspect on the surface of the non-magnetic sleeve.